Flooding is a natural phenomenon that has long shaped the Earth, shaping the landscape and providing fertile regions like the floodplains of rivers and streams. Floods occur when rain falls in quantities greater than what ponds, lakes, riverbeds, and soil can hold and when water is unable to move through the surface of the land quickly enough. This is why the shape of the land influences how often floods can happen, how fast they can rise, and how long they can last.
Floods may also be caused by human activities that obstruct the natural flow and path of rainwater, such as draining wetlands, building paved surfaces that don’t absorb water, or clearing land. Once water reaches a point where it can no longer be contained by ponds, lakes, rivers, or soil, it flows over the land and into streams, rivers, and bays, or into the ocean.
When floodwaters recede, they can leave behind mud and debris that can be expensive to clean up and pose health hazards. In addition, contaminated floodwater can spread diseases that are transmitted through water, such as hepatitis A and cholera. It can also encourage mosquitoes to breed, which can spread malaria.
Even though flooding can cause many problems for humans, it is important to remember that floods are part of the natural cycle. Small seasonal floods are good for fish, depositing sediment on riverbeds where baby fish can grow and carrying nutrients that support aquatic food webs. And wetlands, such as marshes and swamps, that are often flooded, provide vital habitat for a variety of plants and animals.
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